1. Field of the Invention
The present invention relates to a certify testing apparatus and certify testing method, and particularly to a certify testing apparatus and certify testing method for magnetic recording media used in so-called hard disk drives.
Priority is claimed on Japanese Patent Application No. 2007-36293, filed Feb. 16, 2007, the content of which is incorporated herein by reference.
2. Description of the Related Art
Magnetic recording devices typified by hard disk drives are widely used as external memory units of information processing devices such as computers, and in recent years have also come to be used as video recording devices for animated images.
Hard disk drives ordinarily include: a shaft wherein a discoid (donut-shaped) magnetic recording medium with an opening at the center is rotated alone or concentrically in a superimposed plurality (synchronous rotation is conducted in the case of a plurality); a motor which is joined via bearings to the pertinent shaft and which causes rotation of the magnetic recording medium; magnetic heads used for recording and/or playback on both faces of the magnetic recording medium; support arms to which the pertinent heads are attached; and a head stack mechanism which is capable of synchronously moving multiple support arms (this is called a “head stack assembly”), and which causes the magnetic heads to move to desired positions on the magnetic recording medium. The magnetic recording playback heads are ordinarily floating-type heads, and move at a fixed floating height on the magnetic recording medium.
Magnetic recording media loaded into hard disk drives are manufactured by the following process.
After conducting texturing treatment and the like on the surface of a substrate generally composed of aluminum alloy, glass or the like, the magnetic recording medium is prepared by sequentially forming a base layer, magnetic layer, protective layer, lubricating layer, etc. on top of this. Subsequently, a glide testing process and certify testing process are conducted as testing processes of the obtained magnetic recording medium.
The glide testing process is a process which tests whether or not protrusions exist on the surface of a magnetic recording medium. That is, when a magnetic recording medium undergoes recording playback with use of magnetic heads, if there exist protrusions on the surface of the medium with a height equal to or greater than the interval between the medium and the magnetic head, these will cause damage to the magnetic head as it strikes the protrusions, and defects in the medium. In this process, the existence or non-existence of protrusions of such height is tested (e.g., see Patent Document 1, i.e. Japanese Unexamined Patent Application, First Publication No. H10-105908). This process conducts testing for protrusions on the surface of the magnetic recording medium, but recording and playback of signals of the magnetic recording medium are not conducted.
Certify testing is conducted on magnetic recording media which pass the glide testing process. As with the recording and playback of an ordinary hard disk drive, the certify testing process records prescribed signals on a magnetic recording medium with a magnetic head, after which the signals are played back. The quality of the medium—e.g., electrical properties and existence or absence of defects—is then ascertained from the obtained playback signals (e.g., see Patent Document 2, i.e. Japanese Unexamined Patent Application, First Publication No. 2003-257016).
As the certify testing process of magnetic recording media is a testing process that serves to confirm the capability of recording and playback of prescribed signals by a magnetic head as in the recording and playback of a hard disk drive, it tests whether prescribed signals can be correctly read out after they have been written into the magnetic recording medium, in a manner similar to the actual method of use in a hard disk drive.
When the signal processing system of a certify testing apparatus is outlined, a configuration like that of FIG. 7 is obtained.
That is, with respect to a magnetic recording medium in which prescribed magnetic information has been written, a magnetic head 71 sends playback signals that have been read from the magnetic recording medium to downstream circuits, and it is discriminated in these downstream circuits whether or not individual playback bits are errors by having the CMP 78 compare the playback signals and the slice level which is set based on a TAA (Track Average Amplitude=average output of 1 cycle) unit 76.
For example, with the magnetic recording medium of FIG. 8A, when certify testing is conducted on a track having an error area at the location shown by the arrow mark, the playback signals at that time are as shown in FIG. 8B. These playback signals are called envelope signals, and are band-like signals with a constriction at the center. In certify testing, sine wave signals are written into and read from the magnetic recording medium at high frequencies on the order of 50-100 MHz. That is, in the case where testing is conducted in a state where the disk is at a rotational frequency of 6000 rpm, approximately 500,000 or more sinusoidal waveforms are outputted per disk cycle. In the case where the signals pertaining to 1 cycle of a disk in this state are viewed by measuring instrument, band-like signals like that of FIG. 8B are observed.
When a slice level which detects error areas is appropriately set with respect to these playback signals, the location of error area E1 of FIG. 8A can be detected as an error location.
However, in an actual magnetic recording medium, it is often the case that undulations or the like occur over the entire substrate surface and that the substrate surface is not a perfect plane; such undulations or the like render the certify testing of magnetic recording media difficult. For example, considering the case where, as in the magnetic recording medium of FIG. 9A, an undulation occurs which is high in a high output region A1 toward the upper right of the substrate and low in a low output region A2 toward the lower left, and where an error area E2 exists at an upper right position of the substrate, when certify testing is conducted with respect to such a track, the playback signals at that time will be envelope signals like that of FIG. 9B. With respect to the playback signals in this case, even if the slice level which detects error areas is set like that of FIG. 9B in the same way as FIG. 8, it is not possible to detect the location of the allow mark of FIG. 9A as an error location.
The foregoing was presented as a case where undulation occurs in the substrate of a magnetic recording medium as a factor inhibiting detection of an error location in certify testing of a magnetic recording medium, but apart from undulation of the substrate, there are also irregularities in film thickness distribution of the magnetic film of magnetic recording media, and so on.
The present invention was made in light of such circumstances, and its object is to offer a certify testing apparatus and certify testing method which are capable of detecting error locations without being affected by undulation in the substrate of the magnetic recording medium, irregularities in film thickness distribution of magnetic film and the like in certify testing of magnetic recording media.